Lubricating Oil Composition

ABSTRACT

A lubricating oil composition having a low sulfated ash content, a low P content, a low S content and a low Cl content and being favorably employable for lubricating a diesel engine operated using a hydrocarbon fuel oil having a low S content, comprising the following components a) to d) dissolved or dispersed in a base oil having a low S content: a) an ashless dispersant such as alkenyl- or alkyl succinimide or its derivative, b) a calcium alkylsalicylate detergent having a low S content and an organic acid calcium salt, which is an unsulfurized calcium alkylsalicylate detergent having a C 14 -C 18  alkyl group, c) a zinc phosphate anti-wear agent, and d) an oxidation inhibitor.

This application claims priority to Japanese Patent Application numberJP 2010-201230 which was filed on Sep. 8, 2010.

FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition favorablyemployable for lubricating an internal combustion engine operatedoverland such as a diesel engine, a gasoline engine or a gas engine. Inmore detail, the invention relates to a lubricating oil composition forinternal combustion engines which has a low sulfated ash content, a lowphosphorus content and a low sulfur content and shows good hightemperature detergency and anti-wear performance, and which gives lessadverse effects to an exhaust gas cleaning apparatus such as aparticulate filter or an oxidation catalyst mounted on a car foroxidizing unburnt soot, fuel and lubricating oil contained in exhaustedgas, so that the lubricating oil composition can comply with therecently adopted severe exhaust gas requirements and further can complywith more severe exhaust gas requirements which are probably adopted infuture.

In particular, the invention provides an environment friendlylubricating oil composition for internal combustion engines which isfavorably employable with vehicles operated using hydrocarbon fuel oilhaving a sulfur content of not more than approximately 0.005 wt. %,particularly not more than approximately 0.001 wt. %, specificallydiesel engine-mounted vehicles equipped with exhaust gas-cleaningapparatuses such as a particulate filter and an oxidation catalyst.

BACKGROUND OF THE INVENTION

Recently, it has become very important for overland-running dieselengine mounted vehicles to reduce environmental pollution caused byexhaust gas components such as particulates and NO_(x). It is known thatthe pollution can be reduced by mounting exhaust gas-cleaningapparatuses such as a particulate filter and an oxidation catalyst ontothe vehicles. It is noted, however, that the particulate filter isplugged with metal oxides, sulfated ash and carboxylic acids produced bythe combustion of the conventional lubricating oil compositions having ahigh sulfated ash content, a high phosphorus content and a high sulfurcontent, though the soot adsorbed on the filter are removed by oxidationand burning in the exhaust gas cleaning apparatus.

In addition, it is now required to reduce the sulfur content in a fueloil because the sulfur in the fuel oil is burnt to produce unfavorableproducts such as sulfuric acid and sulfate in the exhaust gas whichgives adverse effects to the oxidation catalyst. For instance, thesulfur content of diesel fuel oils for diesel engine-mounted vehicleshas decreased from not more than approximately 0.005 wt. % to not morethan approximately 0.001 wt. %. When the sulfur content in the fuel oildecreases, the content of the metal-containing detergent serving forneutralizing the sulfuric acid or the like in the lubricating oilcomposition can be decreased. It is known that a portion of thelubricating oil composition is burnt in the engine and incorporated intothe exhaust gas. Therefore, it is preferred that the metal content andsulfur content in the lubricating oil composition be as low as possible.Moreover, it is preferred that the phosphorus content in the lubricatingoil composition is decreased so as to keep the catalyst fromdeteriorating. Furthermore, it is preferred that the chlorine content inthe lubricating oil composition is decreased so as to keep the exhaustgas from being contaminated with dioxine.

Heretofore, the diesel engines employed overland for motor cars,construction machines and electric generators have been operatedgenerally using a fuel oil (light oil or heavy oil) having a sulfurcontent of approximately 0.005 wt. % or more and a lubricating oilcomposition having a sulfated ash content of approximately 1.3 to 2 wt.%, a sulfur content of approximately 0.3 to 0.7 wt. %, and a phosphoruscontent of approximately 0.1 to 0.13 wt. %.

JPA 2002-53888 (corresponding to US 2002/0019320 A1) discloses alubricating oil composition which satisfies the recent requirements oflow sulfated ash content, low phosphorus content, low sulfur content andlow chlorine content, which is employable for diesel engines operatedusing a fuel oil having a low sulfur content. In more detail, JPA2002-53888 discloses a lubricating oil composition having a sulfurcontent of 0.01 to 0.3 wt. %, and a phosphorus content of 0.01 to 0.1wt. %, and giving a sulfated ash in the range of 0.1 to 1 wt. %, whichcomprises:

a) a major amount of a mineral base oil having a sulfur content of atmost 0.1 wt. %, preferably at most 0.03 wt. %;

b) an ashless dispersant comprising an alkenyl- or alkyl-succinimide ora derivative thereof in an amount of 0.01 to 0.3 wt. % in terms of anitrogen atom content;

c) a metal-containing detergent containing an organic acid metal saltwhich is selected from the group consisting of a non-sulfurized alkalimetal or alkaline earth metal salt of an alkylsalicylic acid having aTBN of 10 to 350 mg KOH/g and a non-sulfurized alkali metal or alkalineearth metal salt of an alkylphenol derivative having a Mannich basestructure, in an amount of 0.1 to 1 wt. % in terms of a sulfated ashcontent;

d) a zinc dialkyldithiophosphate in an amount of 0.01 to 0.1 wt. % interms of a phosphorus content; and

e) an oxidation inhibitor selected from the group consisting of a phenolcompound and an amine compound in an amount of 0.01 to 5 wt. %,

wherein the amount is calculated based on the amount of the lubricatingoil composition.

It is further described that a preferred metal-containing detergent isan alkali metal salt or an alkaline earth metal salt of unsulfurizedalkylsalicylic acid having an alkyl group having a mean carbon atomnumber of approximately 8 to 30.

In the recently established JASO M 355:2008 (for lubricating oil forautomotive diesel engines), it is described that the lubricating oilaccording to DH-2-08 for trucks and buses equipped with a post-treatmentapparatus for complying with the exhaust gas regulation ought to have asulfated ash content of 1.0±0.1 wt. %, a phosphorus content of not morethan 0.12 wt. %, a sulfur content of not more than 0.5 wt. % and achlorine content of not more than 150 ppm.

It is an object of the present invention to provide a lubricating oilcomposition for internal combustion engines, which satisfies therequirements of the abovementioned JASO M 355:2008 and shows improvedhigh temperature detergency at 300° C. or higher, as compared with thelubricating oil composition disclosed in the aforementioned JPA2002-53888, so as to sufficiently comply with the anticipated moresevere engine operation conditions such as operations at elevatedtemperatures.

SUMMARY OF THE INVENTION

The present inventors have studied the lubricating oil compositiondescribed in JPA 2002-53888 for improving the high temperaturedetergency attained by the disclosed lubricating oil composition andfound that the improved high temperature detergency at temperatures of300° C. or higher is accomplished by a lubricating oil composition inwhich an unsulfurized calcium alkylsalicylate detergent having an alkylgroup having 14 to 18 carbon atoms is employed for the unsulfurizedalkaline earth metal alkylsalicylate having an alkyl group having a meancarbon atom number of approximately 8 to 30. The so formulatedlubricating oil composition shows a satisfactorily good anti-wearperformance and a satisfactorily low viscosity at low temperatures sothat the lubricating oil composition is favorably employable in colddistricts. The present invention has been made on this finding by thepresent inventors.

Accordingly, the present invention resides in a lubricating oilcomposition for lubricating an internal combustion engine which isoperated by the use of a fuel oil having a sulfur content of not morethan 0.005 wt. %, particularly not more than 0.001 wt. %, comprising thefollowing components a) to d) dissolved or dispersed in a base oilhaving a sulfur content of not more than 0.1 wt. %, preferably not morethan 0.03 wt. %, and has a sulfated ash content in a range of 0.1 to 1.1wt. %, a phosphorus content in a range of 0.01 to 0.12 wt. %, a sulfurcontent in a range of 0.01 to 0.5 wt. % and a chlorine content of notmore than 150 ppm:

a) an ashless dispersant in an amount of 0.01 to 0.3 wt. % in terms of anitrogen content, the ashless dispersant being selected from the groupconsisting of an alkenyl succinimide, an alkyl succinimide, orderivatives thereof;

b) a calcium alkylsalicylate detergent in an amount of 0.1 to 1 wt. % interms of a sulfated ash content, the calcium alkylsalicylate detergenthaving a sulfur content of not more than 3 wt. % and a total base numberin the range of 10 to 350 mg KOH/g, containing an organic acid calciumsalt under the condition that the lubricating oil composition containsthe organic acid calcium salt in an amount of 0.2 to 7 wt. %, preferably0.5 to 5 wt. %, more preferably 1.0 to 3 wt. %, based on the amount ofthe oil composition, and comprising an unsulfurized calciumalkylsalicylate detergent having an alkyl group having 14 to 18 carbonatoms;

c) a zinc phosphate anti-wear agent in an amount of 0.01 to 0.12 wt. %in terms of a phosphorus content, the zinc phosphate being selected fromthe group consisting of a zinc dialkyldithiophosphate and a zincdihydrocarbylphosphate, and

d) an oxidation inhibitor in an amount of 0.01 to 5 wt. %, the oxidationinhibitor being selected from the group consisting of an oxidationinhibiting phenol compound and an oxidation inhibiting amine compound,

wherein the sulfated ash content, phosphorus content, sulfur content,and the wt. % given in a) to d) above are values based on the amount ofthe lubricating oil composition.

The lubricating oil composition of the invention has a low sulfated ashcontent, a low phosphorus content and a low sulfur content similar tothose of the lubricating oil composition disclosed in the aforementionedJPA 2002-53888 but shows an improved high temperature detergency attemperatures of 300° C. or higher. Further, the lubricating oilcomposition of the invention shows a satisfactorily good anti-wearperformance. Furthermore, the lubricating oil composition of theinvention shows a satisfactorily low viscosity at low temperatures, sothat the lubricating oil composition can be favorably employed in colddistricts.

Therefore, the lubricating oil composition of the invention isparticularly favorably employable for lubricating diesel engines whichare mounted onto motor cars equipped with exhaust gas cleaning apparatussuch as a particulate filter and an oxidation catalyst and which areoperated in cold districts, using a hydrocarbon fuel oil having a sulfurcontent of not more than approx. 0.005 wt. %, specifically not more thanapprox. 0.001 wt. %.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments of the invention are set forth below.

(1) The calcium alkylsalicylate detergent of the component b) has atotal base number in the range of 30 to 300 mg KOH/g.

(2) The unsulfurized calcium alkylsalicylate detergent having an alkylgroup having a carbon atom number of 14 to 18 has a total base number inthe range of 100 to 250 mg KOH/g.

(3) The ashless dispersant of the component a) comprises succinimide ora derivative thereof which is obtained by a reaction of apolybutenylsuccinic anhydride with a polyamine, the polybutenylsuccinicanhydride being obtained by a thermal reaction of polybutene and maleicanhydride in the absence of chlorine or a chlorine-containing compound.

(4) The lubricating oil composition contains a molybdenum-containingcompound in an amount of 0.01 to 5 wt. %.

(5) The lubricating oil composition has a total base number in the rangeof 1 to 17 mg KOH/g, specifically 2 to 13 mg KOH/g.

(6) The lubricating oil composition is a multigrade engine oilcontaining a viscosity index improver and is an oil of 0W5, 0W10, 0W15,0W20, 0W30, 5W20, 5W30, 10W20, or 10W30.

(7) The lubricating oil composition is employed for lubricating a dieselengine operated using a fuel oil having a sulfur content of not morethan 0.005 wt. %, specifically not more than 0.001 wt. %, in which thediesel engine is mounted on an overland-running vehicle.

The invention further resides in a method for operating a diesel engineby the use of a fuel oil having a sulfur content of not more than 0.005wt. %, specifically not more than 0.001 wt. %., and a lubricating oilcomposition of the invention, the diesel engine being mounted on anoverland-running vehicle.

Base Oil

The base oil employable for the lubricating oil composition generally isa mineral oil or a synthetic oil having a kinetic viscosity of 2 to 50mm²/s at 100° C. and the sulfur content is not more than 0.1 wt. %,preferably not more than 0.03, more preferably not more than 0.005 wt.%.

The mineral oil can be produced by processing a lubricating oil gradedistillate by solvent refining and/or hydrotreating or hydrocracking.Preferably employed is a super-hydrogenating base oil, such as, a baseoil having a viscosity index in the range of 100 to 150, an aromaticcontent of 5 wt. % or lower, and nitrogen and sulfur contents of 50 ppmor lower. Particularly preferred is a high viscosity index base oilhaving a viscosity index of 140-160 which is obtainable by hydrogenationand isomerization of slack wax or GTL wax.

A synthetic oil (synthetic base oil) can be poly-α-olefin, namely apolymer of α-olefin having a carbon atom number of 3-12; dialkyl esterswhich are esters of a dibasic acid such as sebacic acid, azelaic acid oradipic acid with an alcohol having a carbon atom number of 4-18, forinstance, dioctyl sebacate; polyol esters of 1-trimethylolpropane orpentaerithritol with a monobasic acid having a carbon atom number of3-18; or an alkylbenzene having an alkyl group having a carbon atomnumber of 9-40. The synthetic oil is favorably employable, because thesynthetic oil generally has almost no sulfur content and shows highoxidation stability and high thermal stability at high temperatures, andfurther produces less amounts of residual carbonaceous material andsoots.

The mineral base oil and synthetic base oil can be employed singly.However, a combination of two or more mineral base oils and acombination of two or more synthetic base oils can be employed. Inaddition, a mineral base oil and a synthetic base oil can be employed incombination in an optionally determined ratio.

Other Lubricating Oil Additives

The ashless dispersant employed in the lubricating oil composition ofthe invention as the component b) can be an alkenyl succinimide, analkyl succinimide, or a derivative thereof, in which the alkenyl groupand alkyl group can be derived from polyolefin. The ashless dispersantis incorporated into the lubricating oil composition in an amount of0.01 to 0.3 wt. % in terms of the nitrogen content. The percent is givenper the amount of the lubricating oil composition. A representativesuccinimide can be obtained by the reaction between succinic anhydridehaving a substituent group of a high molecular weight alkenyl or alkylwith a polyalkylene polyamine having a mean nitrogen atom number of 4 to10, preferably 5 to 7. The high molecular weight alkenyl or alkyl ispreferably derived from polybutene having a number average molecularweight of approx. 900 to 3,000.

In the process for producing a polybutenyl succinic anhydride by thereaction of polybutene and maleic anhydride, a chlorination procedure isgenerally employed. However, the chlorination procedure gives aremaining chlorine in the product, and hence the finally producedsuccinimide inevitably contains a large amount (such as approx. 2,000 to3,000 ppm) of the emigrated chlorine. In contrast, the thermal reactionusing no chlorine gives a final product having an extremely smallchlorine content (such as 0 to 30 ppm). Therefore, the succinimidederived from a polyisobutenyl succinimide obtained by the thermalreaction can be favorably employed for formulating a lubricating oilcomposition having a low chlorine content such as 0 to 30 wt. ppm. Thesuccinimide can be post-treated with boric acid, a boron-containingcompound, alcohol, aldehyde, ketone, alkylphenol, cyclic carbonate or anorganic acid. Preferred is a borated alkenyl- (or alkyl-) succinimidewhich is obtained by the post-treatment with boric acid or aboron-containing compound and which shows high thermal stability andhigh oxidation stability.

In the lubricating oil composition, the alkenyl- or alkyl-succinimide orits derivative is necessarily contained. However, other ashlessdispersants such as alkenylbenzyl compounds or alkenyl succinic esterscan be employed in combination with the alkenyl- or alkyl-succinimide orits derivative.

The calcium alkylsalicylate detergent of the component b) necessarilycontained in the lubricating oil composition of the invention containsan organic acid calcium salt to give the lubricating oil compositioncontaining the organic acid calcium salt in an amount of 0.2 to 7 wt. %,preferably 0.5 to 5 wt. %, more preferably 1.0 to 3 wt. %, and comprisesan unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 14 to 18 carbon atoms. In the invention, the “unsulfurizedcalcium alkylsalicylate detergent having an alkyl group having 14 to 18carbon atoms” is used to mean an unsulfurized calcium alkylsalicylatedetergent having an alkyl group in which at least 90 molar % of thealkyl group has 14 to 18 carbon atoms.

In the lubricating oil composition, an unsulfurized calciumalkylsalicylate detergent having an alkyl group having 20 to 28 carbonatoms can be used in combination with the unsulfurized calciumalkylsalicylate detergent having an alkyl group having 14 to 18 carbonatoms. The “unsulfurized calcium alkylsalicylate detergent having analkyl group having 20 to 28 carbon atoms” is used to mean anunsulfurized calcium alkylsalicylate detergent having an alkyl group inwhich at least 90 molar % of the alkyl group has 20 to 28 carbon atoms.

The unsulfurized calcium alkylsalicylate detergent preferably is acalcium alkylsalicylate prepared from an alkyl phenol (which is preparedfrom α-olefin having the desired carbon atom number and phenol) by wayof Kolbe-Schmitt reaction. Generally, an overbased calcium salicylatewhich is obtained by way of the carbonation process using slaked limeand carbon dioxide gas for overbasing is used as the calcium salicylatedetergent.

Otherwise, the calcium alkylsalicylate can be directly produced bycarbonizing an alkylphenol calcium salt obtained by directneutralization.

The metal-containing detergent may contain a small amount of an organicacid having a carbon-nitrogen bonding or an alkali metal salt or analkaline earth metal salt of a phenol derivative. Generally, ametal-containing detergent can have an increased base number byattaching an amine compound by reaction so that the base number derivedby the basic nitrogen atom of the amine compound can contribute increaseof the base number of the detergent. Therefore, a metal-containingdetergent having a low sulfated ash but a high base number can beobtained. For instance, there may be mentioned various compounds such asa metal salt of an aminocarboxylic acid. Particularly, there can bementioned an unsulfurized alkylphenate (alkali metal salt or alkalineearth metal salt) having a Mannich base structure. This compound can beprepared from an alkylphenol, formaldehyde, and an amine or an aminatedcompound via Mannich reaction to as to aminomethylate the phenol ringand subsequently neutralizing the reaction product with a base such ascalcium hydroxide.

In addition to the heretofore described metal-containing detergents, asmall amount of sulfonates such as alkali metal salts or alkaline earthmetal salts of petroleum sulfonic acid, alkylbenzenesulfonic acid oralkyltoluenesulfonic acid can be employed in combination with thealkylsalicylate detergent.

The sulfurized phenate which has been used for the conventional dieselengine oils is an alkali metal salt or an alkaline earth metal salt of asulfurized alkylphenol. Typically, calcium salt and magnesium salt areemployed. The sulfurized phenate shows high thermal stability butgenerally has a high sulfur content such as approx. 3 wt. % or more,which is brought about by the sulfurization reaction. In the invention,a small amount of the sulfurized phenate may be employed in combinationwith the alkylsalicylate detergent.

In the lubricating oil composition of the present invention, the twocalcium alkylsalicylate detergents can be incorporated in combinationunder the condition that the organic acid calcium salts contained inthese detergents are incorporated to give a lubricating oil compositioncontaining the organic acid calcium salt in an amount of 0.2 to 7 wt. %,preferably 0.5 to 5 wt. %, more preferably 1.0 to 3 wt. %, based on theamount of the lubricating oil composition. The amount of the organicacid calcium salt can be adjusted by adjusting the content of theorganic acid calcium salt in the detergent and/or adjusting the amountof the detergent to be incorporated into the lubricating oilcomposition.

It is known that the calcium alkylsalicylate detergent is an oilydispersion comprising an organic acid calcium salt (generally referredto as “soap content”) and aggregated basic inorganic salt particles(typically calcium carbonate particles) surrounding the organic calciumsalt dispersed in the oily medium (generally contained in an amount ofapprox. 25 to 55 wt. %). The amount of the organic acid calcium salt inthe lubricating oil composition is important for keeping the hightemperature detergency (ability for keeping the inside of the engineoperated at high temperatures clean) at a high level.

The zinc phosphate anti-wear agent of the component c) is selected fromthe group consisting of a zinc dialkyldithiophosphate and a zincdihydrocarbylphosphate. These zinc phosphate anti-wear agents are wellknown, so far as their preparation methods and properties. The zincphosphate anti-wear agent is employed in an amount of 0.01 to 0.12 wt. %in terms of a phosphorus content. However, the amount preferably is inthe range of 0.01 to 0.06, so as to decrease the phosphorus content andsulfur content in the lubricating oil composition.

The zinc dialkyldithiophosphate preferably has an alkyl group having acarbon atom number of 3 to 18 or an alkylaryl group having an alkylgroup of a carbon atom number of 3 to 18. Particularly preferred is azinc dialkyldithiophosphate having an alkyl group derived from asecondary alcohol having a carbon atom number of 3 to 18 or having analkyl group mixture derived from a mixture of a primary alcohol having acarbon atom number of 3 to 18 and a secondary alcohol having a carbonatom number of 3 to 18, both of which bring about very good anti-wearperformance. The zinc dialkyldithiophosphate derived from the primaryalcohol shows high thermal stability. These zinc dithiophosphates can beemployed alone but can be employed in combination which mainly compriseone derived from the secondary alcohol and one derived from the primaryalcohol.

The lubricating oil composition of the present invention furthercontains an oxidation-inhibiting phenol compound and/or anoxidation-inhibiting amine compound in an amount of 0.01 to 5 wt. %,preferably in an amount of 0.1 to 3 wt. %. Generally, a lubricating oilcomposition having a low sulfated ash content, a low phosphorus contentand a low sulfur content contains decreased amounts of ametal-containing detergent and a zinc dithiophosphate, and hence showsdecreases in high temperature detergency, oxidation stability and wearresistance. In order to improve these decreases, it is required toincorporate the component d) into the lubricating oil composition. Thecomponent d) preferably is a diarylamine oxidation inhibitor and/or ahindered phenol oxidation inhibitor. The incorporation of theseoxidation inhibitor is effective to improve the high temperaturedetergency. From one aspect, the diarylamine oxidation inhibitor ispreferred because it shows a base number derived from the containednitrogen. From other aspect, the hindered phenol oxidation inhibitor ispreferred because it efficiently inhibit oxidation caused by NO_(x).

Examples of the hindered phenol oxidation inhibitors include2,6-di-t-butyl-p-cresol, 4,4′-methylenebis(2,6-di-t-butylphenol),4,4′-methylenebis(6-t-butyl-o-cresol),4,4′-isopropylidenebis(2,6-di-t-butylphenol),4,4′-bis-(2,6-di-t-butylphenol), 2,2′-methylenebis(4-methyl-6-t-butylphenol),4,4′-thiobis(2-methyl-6-t-butylphenol),2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphen-yl)propionate],octyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate and octadecyl3-(3,5-di-t-butyl-4-hydroxyphen-yl)propionate.

Examples of the diarylamine oxidation inhibitors include analkyldiphenylamine having a mixed alkyl group having 4 to 9 carbonatoms, p,p′-dioctyldiphenylamine, phenyl-α-naphthylamine,phenyl-β-naphthylamine, alkylated α-naphthylamine, and alkylatedphenyl-α-naphthylamine.

Each of the hindered phenol oxidation inhibitor and diarylamineoxidation inhibitor can be employed alone or in combination. Optionally,other oil-soluble oxidation inhibitors can be used in combination withthe abovementioned oxidation inhibitors.

The lubricating oil composition of the present invention may furthercontain a multi-functional additive such as molybdenum-containingcompound and/or a hydrated alkali metal borate in an amount of not morethan 5 wt. %, particularly in an amount of 0.01 to 5 wt. %, per each.Most of these compounds have a sulfated ash content and a sulfurcontent. Therefore, the amount can be adjusted in consideration of thesulfated ash content and sulfur content of the resulting lubricating oilcomposition.

The molybdenum-containing compound serves mainly as a friction modifier,an oxidation inhibitor and an anti-wear agent in the lubricating oilcomposition, and further serves to improve the high temperaturedetergency. The molybdenum-containing compound is preferablyincorporated into the lubricating oil composition in an amount of 10 to2,500 ppm in terms of a molybdenum metal content. Examples of themolybdenum-containing compounds include sulfur-containingsuccinimide-molybdenum complex compounds, sulfurized oxymolybdenumdithiocarbamates, sulfurized oxymolybdenum dithiophosphates, anamine-molybdenum complex compound, oxymolybdenum diethylatetamides, andoxymolybdenum monoglycerides. Particularly, the succinimide-molybdenumcomplex compound is effective to give improved high temperaturedetergency.

The hydrated alkali metal borate is effective in giving improved hightemperature detergency and increased base number to the lubricating oilcomposition. The hydrated alkali metal borate can be prepared by theprocesses disclosed U.S. Pat. Nos. 3,929,650 and 4,089,790. Preferred isa dispersion in which micro particles of an alkali metal borate aredispersed which can be prepared by carbonizing neutral alkali metal oralkaline earth metal sulfonate in the presence of an alkali metalhydroxide to give an overbased sulfonate and reacting the overbasedsulfonate with boric acid. In the carbonation reaction, an ashlessdispersant such as succinimide is preferably present in the reactionmixture. The alkali metal preferably is potassium or sodium. In moredetail, particles of a product having a constitutional formula ofKB₃O₅.H₂O and a mean diameter of approximately 0.3 μm or less which aredispersed in a mixture of neutral calcium sulfonate and succinimidedetergent can be mentioned. In consideration of resistance to water,potassium can be replaced with sodium.

The lubricating oil composition of the present invention preferablycontains a viscosity index improver in an amount of 20 wt. % or less,more preferably in an amount of 1 to 20 wt. %. Examples of the viscosityindex improvers include polymers such as polyalkyl methacrylate,ethylene-propylene copolymer, styrene-butadiene copolymer andpolyisoprene. A dispersant type viscosity index improver or amulti-functional viscosity index improver obtained by attaching adispersable group to the viscosity index improving polymer. Theviscosity index improver can be employed singly or in combination.

The lubricating oil composition of the present invention can furthercontain a variety of auxiliary additives. Examples of the auxiliaryadditives include zinc dithiocarbamate,methylenebis(dibutyldithiocarbamate), an oil-soluble copper compound, asulfur compound (such as sulfurized olefin, sulfurized ester orpolysulfide), phosphate ester, phosphite ester, and organic amidecompounds (e.g., oleylamide), which can serve as oxidation inhibitors oranti-wear agents. Further, benzotriazole compounds and thiadiazolecompounds which serve as metalinactivaters can be incorporated.Furthermore, a polyoxyalkylene type nonionic surfactant such aspolyoxyethylene alkylphenyl ether or a copolymer of ethylene oxide andpropylene oxide, which serves as a rust inhibitor or an anti-emulsifier.Furthermore, various amines, amides, amine salts or their derivatives,or fatty acid esters of a polyvalent alcohol or their derivatives, whichcan serve as friction modifiers can be incorporated. A variety ofcompounds which can serve as defoaming agents or pour point depressantscan be incorporated. These auxiliary additives are preferablyincorporated into the lubricating oil composition in an amount of notmore than 3 wt. %, preferably in an amount of 0.001 to 3 wt. %.

EXAMPLES

The present invention is further described by the following illustrativenon-limiting working examples.

(1) Preparation of Lubricating Oil Compositions

The lubricating oil compositions for evaluating their performances wereprepared from the below-mentioned base oil and additives, to givelubricating oil composition having a sulfated ash content of 1.0 wt. %,a phosphorus content of 0.09 wt. %, a sulfur content of 0.2 wt. % and achlorine content of less than 5 ppm. To the lubricating oil compositionwas added a viscosity index improver to have a viscosity grade (SAEviscosity grade) of 5W30.

(2) Base Oil and Additives

1) Base oil (a mixture of the following Base oil A and Base oil B in avolume ratio of 35:65)

Base oil A: Super-hydrogenated base oil (kinematic viscosity at 100° C.:4.0 mm²/s, viscosity index: 123, sulfur content: less than 0.001 wt. %)

Base oil B: Super-hydrogenated base oil (kinematic viscosity at 100° C.:6.5 mm²/s, viscosity index: 132, sulfur content: less than 0.001 wt. %)

2) Additives

Dispersant A: Ethylene carbonate post-treated succinimide dispersant(nitrogen content: 0.85 wt. %, chlorine content: 30 wt.ppm) preparedaccording to the procedure described in Example 17 of JP 7-150166 A, bythe steps of reacting polybutene having a number average molecularweight of approx. 2,200 with maleic anhydride under the thermal reactionconditions; reacting the reaction product with polyalkylenepolyaminehaving an average nitrogen atom number of 6.5 (per molecule) to givebis-type succinimide, and treating the succinimide with ethylenecarbonate: 0.0085 wt. % (amount in terms of nitrogen content)

Dispersant B: Boron-containing succinimide dispersant (nitrogen content:1.5 wt. %, boron content: 0.5 wt. %, chlorine content: less than 5wt.ppm) prepared according to the procedure described in Example 8 of JP7-150166 A, by the steps of reacting polybutene having a number averagemolecular weight of approx. 1,300 with maleic anhydride under thethermal reaction conditions; reacting the reaction product withpolyalkylenepolyamine having an average nitrogen atom number of 6.5 (permolecule) to give bis-type succinimide, and treating the succinimidewith boric acid: 0.06 wt. % (amount in terms of nitrogen content).

Calcium alkylsalicylate detergent (described hereinafter in Examples 1to 4 and Comparison Example 1): 0.82 wt. % (amount in terms of sulfatedash content)

ZnDTP: Zinc dialkyldithiophosphate (P: 7.2 wt. %, Zn: 7.85 wt. %, S:14.4 wt. %, derived from secondary alcohol having 3 to 8 carbon atoms):0.09 wt. % (amount in terms of P content)

Oxidation inhibitor A: Amine compound (dialkyldiphenylamine (alkyl:mixture of C₄ alkyl and C₈ alkyl), N: 4.6 wt. %, TBN: 180 mg KOH/g): 0.7wt. %

Oxidation inhibitor B: Phenolic compound (octyl3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate): 0.7 wt. %

Mo-containing compound: Sulfurized oxymolybdenum-succinimide complexcompound (Mo: 5.4 wt. %, S: 3.7 wt. %, TBN: 45 mg KOH/g): 0.85 wt. %

Viscosity index improver: Non-dispersant type ethylene-propylenecopolymer, Paratone 8057)

Example 1

A lubricating oil composition (TBN: 9.6 mg KOH/g, organic acid calciumsalt content: 1.5 wt. %) was prepared using the following calciumalkylsalicylate detergent:

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 14 to 18 carbon atoms (TBN 220 mg KOH/g, petroleum mediumcontent: approx. 30 wt. %, organic acid calcium salt content: 49 wt. %)

Example 2

A lubricating oil composition (TBN: 9.6 mg KOH/g, organic acid calciumsalt content: 1.5 wt. %) was prepared using the following calciumalkylsalicylate detergent:

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 14 to 18 carbon atoms (TBN 225 mg KOH/g, petroleum mediumcontent: at most approx. 30 wt. %, organic acid calcium salt content: 51wt. %)

Comparative Example 1

A lubricating oil composition (TBN: 9.6 mg KOH/g, organic acid calciumsalt content: 1.2 wt. %) was prepared using the following calciumalkylsalicylate detergent:

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 20 to 28 carbon atoms (TBN 230 mg KOH/g, petroleum mediumcontent: approx. 32 wt. %, organic acid calcium salt content: 42.5 wt.%)

The determination of the organic acid calcium salt content (soapcontent) and evaluation of high temperature detergency was made by thefollowing methods.

(1) Determination of Organic Acid Calcium Salt Content (Soap Content)

The detergent was subjected to the conventional dialysis using rubbermembrane to separate mineral oil and low molecular weight componentsout. The remaining residue (A) was an effective detergent component.Separately, the carbon dioxide content of the detergent was determined.Based on the carbon dioxide content and a separately determined calciumcontent, the content of calcium carbonate (overbasing component content(B)) was determined. The organic acid calcium salt (soap component) wascalculated by subtracting (B) from (A).

(2) Evaluation of High Temperature Detergency

The lubricating oil composition was subjected to the below-mentioned hottube test (KES-07-803) at 300° C. and 305° C.

A glass tube (inner diameter: 2 mm) was placed in a heater blockvertically. In the glass tube, the lubricating oil composition and airwere supplied from the bottom of the tube at rates of 0.31 cc/hr. and 10cc/min., respectively. The supply was continued for 16 hours maintainingthe heater block at the predetermined temperature. After the supply wasterminated, the glass tube was taken out and examined for depositionproduced on the inner surface of the tube. The evaluation was performedon the basis of 10 points (maximum). The 10 point means that nodeposition was observed.

(3) Low Temperature Viscosity

The low temperature viscosity (cP) was determined by means of the MRVviscometer (described in ASTM D4684) at −35° C.

Results of Evaluations and Determination High temp. detergency Low temp.Oil 300° C. 305° C. viscosity Example 1 6.0 6.0 25,200 Example 2 6.5 6.025,100 Comparative 5.0 4.5 Unmeasurable Example 1

As is seen from the above-mentioned results, the lubricating oilcompositions according to the invention (Examples 1 and 2) containingthe calcium alkylsalicylate having an alkyl group having 14 to 18 carbonatoms gave improved high temperature detergency under very severetemperature conditions such as 300° C. and 305° C., and further showed alow viscosity at the low temperature. In contrast, the lubricating oilcomposition of Comparative Example 1 containing only one calciumalkylsalicylate having an alkyl group having 20 to 28 carbon atoms gaveinferior high temperature detergency and could not show a satisfactorilylow viscosity (that is, too viscous to measure) at the low temperature.

Example 3

A lubricating oil composition (TBN: 9.6 mg KOH/g, organic acid calciumsalt content: 1.1 wt. %) was prepared using a 1:1 mixture (in terms ofcalcium content ratio) of the following two calcium alkylsalicylatedetergents:

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 14 to 18 carbon atoms (TBN 220 mg KOH/g, petroleum mediumcontent: approx. 30 wt. %, organic acid calcium salt content: 49 wt. %)

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 20 to 28 carbon atoms (TBN 320 mg KOH/g, petroleum mediumcontent: approx. 35 wt. %, organic acid calcium salt content: 32.5 wt.%)

Example 4

A lubricating oil composition (TBN: 9.6 mg KOH/g, organic acid calciumsalt content: 1.1 wt. %) was prepared using a 1:1 mixture (in terms ofcalcium content ratio) of the following two calcium alkylsalicylatedetergents:

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 14 to 18 carbon atoms (TBN 225 mg KOH/g, petroleum mediumcontent: at most approx. 30 wt. %, organic acid calcium salt content: 51wt. %)

Unsulfurized calcium alkylsalicylate detergent having an alkyl grouphaving 20 to 28 carbon atoms (TBN 320 mg KOH/g, petroleum mediumcontent: approx. 35 wt. %, organic acid calcium salt content: 32.5 wt.%)

The determination of the organic acid calcium salt content (soapcontent) and evaluation of high temperature detergency was made by theaforementioned methods.

Results of Evaluations and Determination High temp. detergency Low temp.Oil 300° C. 305° C. viscosity Example 3 6.0 5.0 25,200 Example 4 6.0 5.025,100

As is seen from the above-mentioned results, the lubricating oilcompositions according to the invention (Examples 3 and 4) containingthe two calcium alkylsalicylates having alkyl groups having differentcarbon atom numbers gave improved high temperature detergency under verysevere temperature conditions such as 300° C. and 305° C., and furthershowed a low viscosity at the low temperature.

1. A lubricating oil composition for lubricating an internal combustionengine which is operated by the use of a fuel oil having a sulfurcontent of not more than 0.005 wt. %, which comprises the followingcomponents a) to d) dissolved or dispersed in a base oil having a sulfurcontent of not more than 0.1 wt. % and has a sulfated ash content in arange of 0.1 to 1.1 wt. %, a phosphorus content in a range of 0.01 to0.12 wt. %, a sulfur content in a range of 0.01 to 0.5 wt. % and achlorine content of not more than 150 ppm: a) an ashless dispersant inan amount of 0.01 to 0.3 wt. % in terms of a nitrogen content, theashless dispersant being selected from the group consisting of analkenyl succinimide, an alkyl succinimide, or derivatives thereof; b) acalcium alkylsalicylate detergent in an amount of 0.1 to 1 wt. % interms of a sulfated ash content, the calcium alkylsalicylate detergenthaving a sulfur content of not more than 3 wt. % and a total base numberin the range of 10 to 350 mg KOH/g, containing an organic acid calciumsalt under the condition that the lubricating oil composition containsthe organic acid calcium salt in an amount of 0.2 to 7 wt. % based onthe amount of the oil composition, and comprising an unsulfurizedcalcium alkylsalicylate detergent having an alkyl group having 14 to 18carbon atoms; c) a zinc phosphate anti-wear agent in an amount of 0.01to 0.12 wt. % in terms of a phosphorus content, the zinc phosphate beingselected from the group consisting of a zinc dialkyldithiophosphate anda zinc dihydrocarbylphosphate, and d) an oxidation inhibitor in anamount of 0.01 to 5 wt. %, the oxidation inhibitor being selected fromthe group consisting of an oxidation inhibiting phenol compound and anoxidation inhibiting amine compound, wherein the sulfated ash content,phosphorus content, sulfur content, and the wt. % given in a) to d)above are values based on the amount of the lubricating oil composition.2. The lubricating oil composition of claim 1, wherein the calciumalkylsalicylate detergent of the component b) has a total base number inthe range of 30 to 300 mg KOH/g.
 3. The lubricating oil composition ofclaim 1, wherein the unsulfurized calcium alkylsalicylate detergenthaving an alkyl group having a carbon atom number of 14 to 18 has atotal base number in the range of 100 to 250 mg KOH/g.
 4. Thelubricating oil composition of claim 1, wherein the ashless dispersantof the component a) comprises succinimide or a derivative thereof whichis obtained by a reaction of a polybutenylsuccinic anhydride with apolyamine, the polybutenylsuccinic anhydride being obtained by a thermalreaction of polybutene and maleic anhydride in the absence of chlorineor a chlorine-containing compound.
 5. The lubricating oil composition ofclaim 1, which contains a molybdenum-containing compound in an amount of0.01 to 5 wt. %.
 6. The lubricating oil composition of claim 1, whereinthe lubricating oil composition has a total base number in the range of1 to 17 mg KOH/g.
 7. The lubricating oil composition of claim 1, whichis a multi-grade engine oil contains a viscosity index improver and isan oil of 0W5, 0W10, 0W15, 0W20, 0W30, 5W20, 5W30, 10W20, or 10W30. 8.The lubricating oil composition of claim 1, which is employed forlubricating a diesel engine operated using a fuel oil having a sulfurcontent of not more than 0.005 wt. %, the diesel engine being mounted onan overland-running vehicle.
 9. A method for operating a diesel engineby the use of a fuel oil having a sulfur content of not more than 0.005wt. % and a lubricating oil composition of claim 1, the diesel enginebeing mounted on an overland-running vehicle.